Turner, P. V., Viscardi, A., Lawli, P. et al. 2014. Evaluation of analgesic efficacy in piglets using a novel pig grimace scale. American Association for Laboratory Animal Science [AALAS] Meeting Official Program, 530 (Abstract #PS12).
There is a critical lack of information surrounding methods to improve the wellbeing of piglets undergoing painful procedures. It is not uncommon for piglets to undergo potentially painful procedures without anesthesia or analgesia, particularly for agricultural research projects. The objectives of this study were to develop and validate a Pig Grimace Scale (PGS) in association with behavioral scoring techniques to assess analgesic efficacy in piglets undergoing castration. Castration was performed on 4 litters of 5-d-old pigs (n = 19)with treatments randomized across litters: no treatment, meloxicam + 531 EMLA, meloxicam + unmedicated cream, saline + EMLA, and saline + unmedicated cream (4 to 5 pigs per group). Pens were videorecorded for 1 h the day prior to castration, immediately after castration for 7 h, and for 1 h at 24 h postprocedure. Thirty behaviors or postures were scored continuously for the first 15 min at −24, 0, 1, 2, 3, 4, 5, 6, 7, and 24 h by an observer blinded to treatment. For PGS scoring, 627 facial images were captured across the 9 time points. Facial action units and an associated scale were developed, including ear position, orbital tightening, and cheek bulge. Three individuals blinded to treatment scored each photo separately. Baseline PGS scores from −24h pigs were subtracted from scores obtained after castration. Data was analyzed using a linear model ANOVA with post hoc Bonferroni tests. Pigs demonstrated significant behavioral changes up to 7 h after castration and the use of meloxicam and EMLA were not associated with a reduction in painful behaviors or postures. No litter-associated differences were noted in behavioral or PGS data and data was combined across litters. There were no treatment differences in PGS scores and PGS scores at 0, 3, 4, and 5 were significantly higher than those at 7 h after castration (F4,15 > 3.06, P < 0.05). These findings indicate that the PGS may be useful for evaluating pain in piglets.